Titanium nitride (TiN) films are widely used in semiconductor devices and ultra-large-scale integrated circuits. For example, TiN films have been used in semiconductor devices as a diffusion barrier for preventing metal diffusion into other materials. TiN films have been employed as a diffusion barrier against copper (Cu) diffusion, for example in contacts, vias and trenches. Other uses include metal wiring, contact plug, and upper electrode of a capacitor that prevents diffusion of dopants and other ions toward a lower region of a semiconductor device, such as toward a gate of a transistor, a dielectric layer of a capacitor, or the semiconductor substrate.
Early deposition methods for TiN films included reactive sputtering using a metallic titanium target and nitrogen gas. These deposition methods suffered from poor step coverage over high-aspect ratio features found in advanced semiconductor devices, thereby requiring development of new deposition methods able to provide conformal deposition of thin TiN films that must be as thin as possible to accommodate the higher aspect ratios of today's devices. The need for conformal deposition has led to chemical vapor deposition (CVD) methods, plasma-enhanced CVD (PECVD), and more recently atomic layer deposition (ALD) and plasma-enhanced ALD (PEALD) methods.
The reaction of TiCl4 and NH3 using substrate temperature in the range of about 500° C. to about 700° C. has commonly been used in a CVD process for depositing TiN films. Reaction byproducts from the CVD process include chlorine that may diffuse into the semiconductor substrate and deteriorate the electronic characteristics of the semiconductor device. More recently new CVD and ALD processes have been developed using other titanium sources such as titanium amide compounds that are free of chlorine and allow lower processing temperatures.
ALD of TiN films is a type of cyclical deposition that refers to sequential introduction of titanium and nitrogen precursors to deposit a thin film onto a substrate. In particular, the deposition may include sequential introduction of a pulse of a titanium precursor, followed by a pulse of a purge gas and/or a pump evacuation, followed by a pulse of a nitrogen precursor, which is followed by a pulse of a purge gas and/or a pump evacuation. Sequential introduction of separate pulses results in alternating self-limiting chemisorption of monolayers of each precursor on the surface of the substrate and forms on the order of a monolayer of deposited TiN in each cycle. The sequential introduction of precursors is repeated as necessary to form a TiN film that has a desired thickness. One drawback of ALD is that the growth rate for TiN can be very low compared to CVD methods. A typical growth rate of an ALD process is 1-2 angstroms (Å) per cycle.
Although these new CVD and ALD processes provide important temperature improvements over chlorine-based processes, they suffer from a variety of problems that make these processes unsatisfactory for advanced semiconductor manufacturing where film conformality, high step coverage over high-aspect ratio structures, and high deposition rate for high volume throughput are required. Accordingly, new processing methods for forming TiN films are required that can overcome these problems and limitations with prior art deposition methods.